The Capsaicin (8-Methyl-N-Vanillyl-6-Nonenamide) is the active pungent of the Solenaceae family plants; it interacts with the umnyelinated C Fibers of the Trigeminal Nerve. The repeated topical application produces a selective and temporary destruction of the unmyelinated C Fibers, desensitizing the nasal cavity against some external stimuli, keeping intact the nasal reflexes.
This effect has been demonstrated by stimulating the nasal cavity in laboratory animals, measuring the levels of Substance P from the nasal secretions, and at the Nucleus of the Trigeminal Nerve in the brain stem.
The Subsance P is a peptide which acts as a neurotransmitter, it is located in large amounts in the nasal cavity, and it is released by the unmyelinated C Fibers of the Trigeminal Nerve in response to a wide variety of stimuli including thermal, mechanical and chemical stimuli.